This invention relates to a stretchable composite fiber, and a yarn and a nonwoven fabric containing such composite fibers.
A composite fiber is known which comprises a stretchable fiber and unstretchable fibers that are made of an elastic polymer and an inelastic polymer, respectively, that are insoluble in each other. The stretchable and unstretchable fibers have first and second exposed surfaces, respectively, that are arranged circumferentially alternately with each other.
It is possible to form a stretchable nonwoven fabric by forming a fiber web from such composite fibers, and stretching the web in at least one direction, thereby separating the stretchable and unstretchable fibers from each other (see JP patent publication 2006-22450). Such a nonwoven fabric is characterized by its improved feel to the touch compared to a nonwoven fabric consisting only of stretchable fibers, because the stretchable fibers, which have a rubber-like feel to the touch, are partially covered by the unstretchable fibers, which feel good to the touch.
But as shown in FIGS. 10A and 10B, a composite fiber 40 used as a material for e.g. a conventional stretchable nonwoven fabric comprises a stretchable fiber 41 and a plurality of unstretchable fibers 42 arranged symmetrically on the outer surface of the stretchable fiber at constant intervals and integrally joined to the stretchable fiber.
Thus, when this composite fiber is stretched, uniform shear stress acts on the interfaces of the stretchable fiber 41 and the respective unstretchable fibers 42, so that the unstretchable fibers 42 are subjected to less strain and thus cannot be efficiently separated from the stretchable fiber. Thus, the unstretchable fibers were often not completely separated from the stretchable fiber. Because separation of the stretchable fibers is incomplete, with the non-stretchable fibers partially joined to the stretchable fiber, the composite fiber 40 is not sufficiently stretchable when stretched.
Because efficiency of separation is low, it was impossible to sufficiently reduce the fineness of the composite fiber 40. This is because if the fineness is increased, the degree of stretchability of the stretchable fiber 41 also decreases, so that it becomes difficult to separate the unstretchable fibers 42 from the stretchable fiber 41.
Also, because the unstretchable fibers 42 are subjected to less strain, they are not crimped so markedly, so that the composite fiber is less bulky even after the unstretchable fibers are separated from the stretchable fiber. Thus, the composite fiber 40 is less voluminous even after it is stretched.
Further, as shown in FIG. 11, because the unstretchable fibers 42 are not sufficiently wrapped around the stretchable fiber 41, the area of the surface of the stretchable fiber 41 that is directly brought into contact with hands and fingers tends to be large, so that this composite fiber still has a rubber-like feel to the touch.
An object of the present invention is to provide a stretchable composite fiber which is high in stretchability, voluminous, good to the touch and can be produced efficiently.